Identification of direct transcriptional targets of Nfatc2 that promote ß-cell proliferation in human islets (ChIP-seq)

The transcription factor Nfatc2 is a potent ß-cell mitogen in mouse and human islets, however, the direct genomic targets that mediate the mitogenic effects have not been identified. We expressed a constitutively active form of Nfatc2, and the closely related Nfatc1, in human islets and identified ~5,600 differentially expressed genes. Nfatc2 binding sites in human islets were identified via ChIP-seq, yielding ~8,600 high-confidence peaks. By integrating gene expression changes induced by Nfatc2 with genomic binding sites for Nfatc2, we identified ~2,200 direct transcriptional targets of Nfatc2 in human islets. Direct targets that were induced by Nfatc2 were enriched for transcripts that regulate the cell cycle, and for motifs associated with the transcription factor FoxP1. We showed that islets from an endocrine-specific FoxP1, FoxP2 and FoxP4 triple-knockout mouse are less responsive to Nfatc2-induced ß-cell proliferation, suggesting the FoxP family may work in concert with Nfatc2 to regulate ß-cell proliferation. Nfatc2 induced ß-cell proliferation in both mouse and human islets, whereas Nfatc1 does so only in human islets. Exploiting this species difference in Nfatc1-responsiveness, we identified ~250 direct transcriptional targets with similar transcriptional profiles. This gene set strongly enriches for cell cycle-associated transcripts, and includes the nuclear hormone receptor, Nr4a1. We show that deletion of Nr4a1 greatly reduces the capacity of Nfatc2 to induce ß-cell proliferation, suggesting that much of the effect on Nfatc2 occurs through its induction of Nr4a1. Integration of ncRNA profiling, chromatin accessibility and Nfatc2 binding sites enabled us to identify key Nfatc2-dependent enhancer loci that mediate enhanced ß-cell proliferation. Overall design: Nfatc2 binding sites were identified in human islets using ChIP-seq after adenoviral transduction of a constitutively active Nfatc2 protein. Six human islets samples were used as biological replicates.